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- #81
I have a question, from a scientific perspective. The best testing would be using test equipment, but lacking such tests or equipment, why wouldn't it be "proper" to use a test frequency (or frequencies) as a listening test to evaluate an amplifier (or system)?
Scientific testing in many cases require a system to be broken into individual smaller systems to provide usable information. In this case a specific frequency test appears to be valid to evaluate the response of the amplifier over a specific (narrow) frequency range. It would seem the argument should be that many additional frequencies should be tested. When music is used, it would seem that evaluating individual frequencies....
Well evaluating the capabilities of something you want to have a margin or a safety factor. If I am stressing a beam I want to stress it with a little bit more than I think I will ever apply to it to see if it breaks. I want to flesh out the envelope of performance. In audio there may not be the safety issue, but you do want some margin beyond your requirements.
Despite what most people imagine, test tones can lay bare the limits of performance in ways music usually doesn't. One of the very toughest test tones is the twin tone IMD test. Two high frequency signals combined to maximum level. One can imagine having 20 tones instead of 2 would be more stressful, but that is not normally the case with amplifiers. One may wish to use a sweep or a series of spot tones to flesh out flatness of frequency response.
So if music is a lesser stressor test tones can give you a margin of performance. Do well on the test tones, and you don't even need to test it with music most of the time. Nor is this unusual in designing products. Many things are designed and tested in sensible ways that don't require use of the product as it will be used to confirm. Sometimes there are gotchas, but more often than not there are none.
As for the idea never have blind tests been done with test tones, well of course they have. People can detect marginally audible distortion at lower levels with tones than they can music. They can more readily detect and detect at smaller levels of difference frequency response differences in gear with pink or white noise. So if listening tests of tones are clean, and wideband noise are clean, you'll be able to use the gear for music knowing all is well. Wideband noise has all the frequencies all the time.